1. Field of the Invention--The present invention relates to a vortex chamber and method for generating aqueous flotation froth.
2. Description of the Prior Art--Froth flotation is well known as a technique for separating minerals from gangue, for example, recovering selected oxides from mineral ores and separating combustible coal from slate. In the froth flotation process, air bubbles are formed beneath the surface of a vat containing an aqueous slurry of particles to be separated in the process. The slurry is agitated and the air bubbles rise to form a froth blanket above the liquid surface. Some of the particles are selectively adhered to the rising air bubbles and are recovered along with froth from the top of the vat. Other particles are withdrawn as an aqueous slurry from the bottom of the vat. In operation the vat requires a source of air bubbles and requires vigorous mechanical agitation of the liquid components of the vat accompanied by minimum agitation of the froth.
The mechanical agitation can be provided by rotating mechanical impellers, by pressurized injection of water or aqueous slurry beneath the liquid level of the vat or by other means (U.S. Pat. No. 3,048,272).
A vortex chamber has been proposed for creating mechanical agitation and generating appropriate air bubbles. Vortex chambers have been employed with success in froth flotation installations. Desirably the air bubbles should be of uniform size and should be distributed uniformly throughout the volume of the vat. Prior art vortex chambers consist of a cylindrical portion mounted above a conical portion having a bottom apex. An outlet is provided in the bottom apex. Water or aqueous slurry is introduced tangentially into the cylindrical portion where it swirls throughout the chamber and exits through the bottom outlet. An opening is provided in the top of the cylindrical portion to receive air which is sucked into the vortex chamber and is formed into small air bubbles as a result of the shearing action occurring as the water or aqueous slurry is forced at high velocities through the bottom opening. The vortex chamber is mounted securely in the central region of a froth flotation vat well below the liquid level of the vat. Another shortcoming of prior art vortex chambers is the directional thrust of the liquid agitation which they generate.
The swirling spray emitted from the bottom opening of the prior art vortex chambers is not uniform around the circumference and consequently the weak side of the spray permits air to escape unsheared, particularly when the shearing capability of the strong side of the spray is approached. Alternatively if the amount of air in the system is restricted to shearing capacity of the weak side of the spray, much of the air shearing capacity of the strong side is unused.
The exiting water or aqueous slurry enters into the vat in a radially outward direction away from the vortex chamber establishing undesirable directional currents within the liquid inventory of the vat. As an example, the single inlet vortex chamber develops an outlet spray which is non-uniform, with the heaviest concentration appearing approximately 270 degrees beyond the inlet. Because of this non-uniformity of slurry flow from the bottom of the vortex chamber, the escaping, unsheared or partially sheared air from the weak side of the device can create a boiling action within the vat at differing locations.